This recent study has caused some headlines, and understandable chatter around the thyroid cancer community, including on the THYCA facebook page.
Should we worry?
Should we use this information to help guide whom to treat with radioiodine?
Does this change what we should be doing?
Not really. I say this because such data is already well known, and is already factored in to many of the best guidelines (such as the American Thyroid Association guidelines). Given the known small risk of death from second cancers (approx 1% lifetime risk) caused by radioiodine (particularly the higher doses of radioiodine), we have to be fairly sure that the radioiodine is resulting in a higher chance of benefit than harm. That is partly why we don't generally recommend radioiodine for those patients with low risk thyroid cancer.
I've also seen questions about whether screening for these second cancers might be a good idea. This raises the issue of how best to screen for such cancers. You have to be careful not to be causing either excessive psychological harm (repeated screening that has low yield can cause psychological harm such as anxiety) or physical harm (radiation from repeated CT scans can also cause cancer - here's an example from the world of adrenal incidentalomas - in a nutshell each CT of the abdomen has about a 1 in 3000 risk of causing death from the associated radiation).
So in summary - yes it's great to have new research than helps inform what the best treatment should be, but his particular study should not cause alarm. Instead it should provide further confidence that clever people (not me!) are continually trying to find the best possible treatments for thyroid cancer and that the move towards giving lower doses of radioiodine and only treating those thyroid cancers at higher risk of causing future ill health is a sound way forward.